Once upon a time, Mark Cuban was not rich. It may be hard for people, especially sports fans, to imagine, but it's true. Once upon a time, he was a young Pittsburgh native just trying to make it in the world.

There are millions of Americans today trying to make it like Cuban, whose net worth, according to Forbes, is $2.5 billion. The business mogul and entrepreneur knows there are others who have the potential to hit it big in business. And he has some advice for them.

Tip No. 1: You don't know everything
In the egotistical world of business, it is easy to get overconfident. Cuban himself was fired from an early job at Your Business Software in Dallas when he went to close a deal at the same time he should have been opening the door.

"When I first got started, I thought I knew everything or that if I didn't know it, I could figure it out in a heartbeat," Cuban told ThePostGame. "I worked hard to learn the things I didn't know, but over the years, I've come to the realization, there are some things I just don't know and that's OK."

Tip No. 2: If you don't know something, seek help
Again, Cuban warns others of being overconfident. Many people think they can do it all, but human error prevents anyone from being perfect. Prospective businessmen and entrepreneurs must expect holes in their knowledge. They must learn to trust others.

"The things I don't know, it's a lot better if I just recognize and accept it and go find someone who can fill that skillset, fulfill that knowledge and complement what I can do," Cuban said. "When I first got started, I tried to do it all."

Tip No. 3: Everyone has ideas
Congratulations, people of the world. Everyone on the planet has come up with some idea they think would make life easier. It's natural.

Maybe you're the guy who has thought of an idea for a hovercraft or a time machine. But have you developed that idea? Only a select group of people invest time in their ideas. What if Mark Zuckerberg didn't build Facebook in his Harvard dorm? What if Bill Gates didn't start Microsoft in his garage? What if Benjamin Franklin didn't fly that kite? These innovators followed through on their ideas. Cuban suggests you do the same.

"Ideas are actually the easiest part," he said. "The hard part is knowing what you need to do and then executing on your plan and then staying focused with it."

Tip No. 4: Focus on your plan
Piggybacking off Tip No. 3, Cuban believes the best businessmen and entrepreneurs are those who put their mind to a project and do not give up. When Cuban looks into a company, whether it be a well-known corporation or a start-up on the reality TV series Shark Tank (he is a panelist), he searches for certain green lights before investing.

"I always look for the same traits," he says. "Has someone done their homework? Are they fully focused on the opportunity? And is the opportunity worthwhile itself?"

Cuban says one of the best skills in business is staying on task. If he finds someone who fits this description, he may take the risk of pulling out his checkbook and putting some money into the individual's company.

"Some of these people allow themselves to get pulled in different directions once they get started (with) their own business," he says. "I look for focus, I look for preparation, I look at the idea, and I look to see if the person can keep it together."

Tip No. 5: Don't invest in sports -- most of the time
"Stay away," Cuban says about those who may want to invest in sports.

It might seem contradictory that Cuban, an NBA owner, strongly advises against investing in sports-related business endeavors, but he can explain. The problem with sports investing is there are actually too many people interested.

"I get so many business ideas and proposals about Internet fan site(s)," Cuban says. "Or another big one I get is people who want to do scouting sites for high school kids. There's just so many of those things."

For those who want to invest in the sports world, Cuban says it needs to be the right scenario, and he insists the speculators need one key ingredient: Capital.

"It's rare that an idea is actually unique in the sports area particularly when it comes to technology, but it always comes down to execution of the idea, having capital to really push it forward," Cuban says.

"Normally I'm not a big believer that capital makes a difference, but if you're going to make the mistake of going into a highly penetrated, highly competitive area like a sport, then you deserve what you get. I typically would not tell anybody to invest in sports in any angle whatsoever."

Tip No. 6: Invest in Diet Mountain Dew
Cuban, a longtime drinker of Diet Mountain Dew, believes in this product so much that he jumped at the chance to tout it in a commercial.

It turned out to be the last commercial from famed director Tony Scott, who committed suicide Sunday.

Cuban's business tips and techniques will be on display for the public this fall. The fourth season of Shark Tank, Cuban's second season as a full-time panelist, will debut Sept. 14 on ABC.

Follow us on Facebook and Twitter to read them first!